Intel explains how the new CPUs can use 7 watts of power, sort of.

If you were reading our CES coverage last week, you'll know that among other things Intel introduced a handful of new, lower-power Y-series Ivy Bridge CPUs designed to fit into thinner and lighter Ultrabooks and tablets. The slides in Intel's keynote called these "7 watt" Ivy Bridge CPUs, and the company compared them directly to the 17 watt U-series chips in wide use today.

After talking to some Intel reps and doing some sleuthing of our own, we found the direct comparison wasn't quite warranted. The actual thermal design power (TDP) of those processors was in fact 13 watts—still lower than before, but less miraculous than had previously been implied. A new measurement, scenario design power (SDP), was actually being used to achieve that 7 watt figure.

There was one particular element of that write-up that was not entirely accurate: based on our conversations with Intel reps, we thought SDP was purely a marketing ploy, a measurement of the amount of power the processor would use on average. It turns out there is an element of marketing to these new 7 watt CPUs, but there's a technical element, too—Intel is simply giving a name to and publicizing a measurement previously left behind-the-scenes. We talked with an Intel engineer to get a better explanation.

TDP explained

To fully understand what's going on here, you need to understand TDP. In Intel's case, a specified chip's TDP has less to do with the amount of power a chip needs to use (or can use) and more to do with the amount of power the computer's fan and heatsink need to be able to dissipate while the chip is under sustained load. Actual power usage can be higher or (much) lower than TDP, but the figure is intended to give guidance to engineers designing cooling solutions for their products.

In laptops especially, balancing power usage and performance is all about sliding clock speeds, active CPU cores, and other values up and down dynamically depending on what the computer is doing. Older mobile processors could simply ramp their clock speeds down when idle to save power, but newer Turbo Boost-equipped CPUs can actually exceed their stated clock speeds (and their TDP) for a short amount of time. The idea is that the sooner the CPU can get its work done, the sooner it can go back into a power-sipping idle state. If the CPU needs to work hard for an extended period of time and the laptop gets warmer, it will slowly ramp down its speed until it's operating at its stated TDP.

There are two OEM-configurable "power level" states that define how quick the CPU can be in these situations: PL2 tells the processor how much power it's allowed to use when it needs a short burst of speed, and PL1 defines how quickly the processor can run under sustained load. Both of these PL states are given in terms of watts, and generally speaking PL1 is set to the CPU's maximum TDP value.

Here's where we start to get closer to what Intel is doing with its Y-series CPUs: for its U-series 17 watt TDP CPUs, Intel actually tests them and validates them for usage at three different PL1 values: 17 watts (the max TDP), 20 watts, and 14 watts. The latter two values aren't officially defined anywhere on the CPUs' official product pages, but they're there for OEMs whose cooling solutions either exceed or undershoot the TDP value.

Under what Intel considers to be "normal" workloads—short bursts of activity followed by a relatively prompt return to an idle state—the same CPU will perform at exactly the same level regardless of the PL1 value set by the OEM. It's under sustained heavy workloads—things like gaming, video and photo editing, crunching big databases, and so on—that the PL1 value makes a difference. Depending on what it's set at, you might have two different laptops using the same processor that actually perform differently under load.

SDP: Taking it one step further

This is at the heart of what Intel is doing with the Y-series processors: their maximum TDP has been lowered four watts, from 17 to 13. Intel is also validating them for use at two lower PL1 values: 10 watts and 7 watts. This is where the marketing we discussed earlier comes in—rather than keeping these values under the covers as it has so far been content to do, Intel has taken that lowest value, put it on its product pages, and called it SDP.

Intel told me that these SDP values are only intended for use with current and future Y-series processors. U-series, M-series, and desktop class processors will continue to use Intel's TDP ratings, at least for the foreseeable future, and while they may be validated for use at lower and higher values it won't be a core part of those CPUs' specifications as it is with the Y-series chips.

For systems that do use these processors, they will enable thinner and longer-lasting laptops and tablets, but they make it more difficult to tell exactly how fast a given PC will be when under sustained load. Short bursts of CPU activity will run equally quickly on a Core i5-3339Y whether the PC OEM sets its PL1 value to the SDP of 7 watts or the full TDP of 13 watts, but for long-running CPU-heavy activities like gaming and video encoding there's a chance that two different PCs running the same processor may perform the same task at different speeds. The near-50-percent drop in TDP is also likely to cause a much more noticeable performance hit than a 17 watt processor with a PL1 value set to 14 watts.

Is any of this deal-breaking? Almost certainly not—even when running at the 7 watt PL1 value, the systems will still be much quicker than anything based on Atom and ARM would be. The increased efficiency will also enable better performance and battery life to even smaller and slimmer devices than we currently have. Even if OEMs stick to the max TDP of 13 watts, you're still saving power over the older 17 watt processors while maintaining performance similar to that found in Sandy Bridge-era Ultrabooks. This is a testament to both the increasing maturity of Intel's 22nm manufacturing process and processor binning, which Intel assured me it was doing in order to find the most power-efficient processors.

It also helps that the tasks that will expose speed discrepancies between systems with disparate PL1 settings are usually best left to beefier systems. Serious gamers, professional video editors, and others to whom top-flight performance is vital will likely want to have larger but faster laptops and desktops to speed those tasks along.

What these processors unfortunately add to the mix is another value the technically savvy need to be aware of when they buy their systems—one that we'll need to be particularly vigilant about in reviews of PCs that use them. Intel isn't being specific about the clock speeds or performance levels we can expect from PCs with differing PL1 values. Instead, we were told, essentially, that we would need to benchmark systems as we received them and find this out ourselves. Especially in PCs using Y-series processors, Ars will be careful to do this in our reviews going forward.

Following Intel lead. I can make your house eco-friendly instantly at very low cost. To encourage yourself to reach a lower "Scenario Electricity Usage" you just need to change all the circuit breakers for a lower wattage. They will now trip at 50% of their former max load. Et voila! the magic "Scenario".

Otherwise Intel gets to pull these types of shenanigans......without much recourse....

I don't see how they're shenanigans. Intel is being rather open about how they came to the 7 watt figure, how they get the chips that meet that figure, and the real TDP for those 7 watt chips.

It's not like my thinkpad had the TDP of the chip on the laptop next to the Core 2 Duo sticker and the Windows Vista sticker. It's not really a number that concerns anyone other than the folks building the system and I'm sure they're taking the true TDP numbers into consideration.

Otherwise Intel gets to pull these types of shenanigans......without much recourse....

I don't see how they're shenanigans. Intel is being rather open about how they came to the 7 watt figure, how they get the chips that meet that figure, and the real TDP for those 7 watt chips.

It's not like my thinkpad had the TDP of the chip on the laptop next to the Core 2 Duo sticker and the Windows Vista sticker. It's not really a number that concerns anyone other than the folks building the system and I'm sure they're taking the true TDP numbers into consideration.

I don't think they're being particularly deceptive, especially given the industry in which they operate. Obviously their intention at their presentation was to compare the 7W SDP number to the 17W TDP number for the U-series chips, but the 13W TDP figure is listed on ARK where anyone can see and Intel PR was very receptive to my questions about how they arrived at the new figure (obviously). I do wish they'd been more open from the start, though.

I'm quite displeased by this bait and switch. Intel has previously announced that OEM's would be getting 10W Ivy Bridge parts. This new announcement of 7W parts are the same 10W parts they were previously boasting about but using a more liberal power consumption measurement. This was compounded that the clarity of the 7W figure is happening well after their presentations at CES. It would have been nice to hear some of this change in how they measure power in the actual presentation of the 7W parts. There is some merit to moving to a 80 degree C thermal maximum for ultra mobile devices (do you want to hold a 105 C device?) and dealing with dynamic power allocation between components on the chip. It also wouldn't be so bad if Intel went back and reevaluated some of their chips using SDP for comparison as well as clearly indicating TDP for these new chips.

Dilbert wrote:

Press release two years from now: Announcing brand new Uber Bridge processors. The Uber Bridge use 7W at full load, unlike our old loser (don't buy!) CPUs which we claimed used 7 W but they really used more. This time really 7W. We promise. With 32 cores*!

Oh..you actually want to USE the device ... well, that'll ramp up to double+ the watts.

Unless I'm misunderstanding the article, it's kind of the opposite... It sounds like the PL2 state is 13W, meaning (for example) you're using 13W for the brief period of time the CPU is working on loading a webpage, but you're using the 7W PL1 state when doing something like gaming or watching/encoding a movie. At least, if the OEM decides to set the PL1 at 7W.

Can anyone confirm if I'm understanding that correctly?

Also, from what I can understand, Intel is actually being transparent about the options they give OEMs for PL1 settings, which is an improvement from before where consumers had no idea what PL1 values were available to OEMs... so why is that shenanigans?

Otherwise Intel gets to pull these types of shenanigans......without much recourse....

I don't see how they're shenanigans. Intel is being rather open about how they came to the 7 watt figure, how they get the chips that meet that figure, and the real TDP for those 7 watt chips.

It's not like my thinkpad had the TDP of the chip on the laptop next to the Core 2 Duo sticker and the Windows Vista sticker. It's not really a number that concerns anyone other than the folks building the system and I'm sure they're taking the true TDP numbers into consideration.

I don't think they're being particularly deceptive, especially given the industry in which they operate. Obviously their intention at their presentation was to compare the 7W SDP number to the 17W TDP number for the U-series chips, but the 13W TDP figure is listed on ARK where anyone can see and Intel PR was very receptive to my questions about how they arrived at the new figure (obviously). I do wish they'd been more open from the start, though.

Andrew, thanks for the clarification; great article. It dissipated a couple of doubts that I had when I read the news yesterday.

Oh..you actually want to USE the device ... well, that'll ramp up to double+ the watts.

Unless I'm misunderstanding the article, it's kind of the opposite... It sounds like the PL2 state is 13W, meaning (for example) you're using 13W for the brief period of time the CPU is working on loading a webpage, but you're using the 7W PL1 state when doing something like gaming or watching/encoding a movie. At least, if the OEM decides to set the PL1 at 7W.

Can anyone confirm if I'm understanding that correctly?

Also, from what I can understand, Intel is actually being transparent about the options they give OEMs for PL1 settings, which is an improvement from before where consumers had no idea what PL1 values were available to OEMs... so why is that shenanigans?

The PL1 value for these chips can be either 7W or 10W or 13W if the OEM wants (other values are possible but Intel told me they only validate these three). The PL2 state CAN be 13W given a PL1 state of 7W, but it can also be higher or lower depending on the PC's ability to dissipate heat.

PL2 is basically how the computer runs when it's sprinting and PL1 is how it runs during a marathon. Does that make any sense?

aagh, just say controlled by oem undervolting and underclocking depending on desired performance envelope.Its still a shenanigan when you give this marketing byword then have to qualify it with an elaborate highly conditional explanation.Its like when my girlfriend catches me looking at women in bikinis at the beach.Then i qualify my answer by saying "im just admiring their fashionable swimwear and not them honey"

ps: forgot to say that she rolls up her eyes and hits me with the beer can anyway.

Oh..you actually want to USE the device ... well, that'll ramp up to double+ the watts.

Unless I'm misunderstanding the article, it's kind of the opposite... It sounds like the PL2 state is 13W, meaning (for example) you're using 13W for the brief period of time the CPU is working on loading a webpage, but you're using the 7W PL1 state when doing something like gaming or watching/encoding a movie. At least, if the OEM decides to set the PL1 at 7W.

Can anyone confirm if I'm understanding that correctly?

Also, from what I can understand, Intel is actually being transparent about the options they give OEMs for PL1 settings, which is an improvement from before where consumers had no idea what PL1 values were available to OEMs... so why is that shenanigans?

The PL1 value for these chips can be either 7W or 10W or 13W if the OEM wants (other values are possible but Intel told me they only validate these three). The PL2 state CAN be 13W given a PL1 state of 7W, but it can also be higher or lower depending on the PC's ability to dissipate heat.

PL2 is basically how the computer runs when it's sprinting and PL1 is how it runs during a marathon. Does that make any sense?

I think so -- I mean, what I described basically lines up with that, right? The one piece I was kind of missing in my description is that the 13W and 7W PL2/PL1 levels are just values the OEM can decide to line up with (or not). If there is something in the way I described it that jumps out at you as wrong, then I think I'm still not quite getting it, but otherwise I think it makes sense.

Also I'm liking *foo's links to the datasheets... way more info than I could ever need, but interesting to get some insight into the details of how this stuff works.

Otherwise Intel gets to pull these types of shenanigans......without much recourse....

Exactly what can AMD do? They have no fab. Much less FABS. They have fired engineers. And will continue to do so as they cut existing multi year projects to grasp at solutions that show no promise.

They are moving away from their traditional strengths into areas that have little chance to actually be profitable all driven by a board of directors that put, essentially, a suit monkey in charge of a very complex business he knows nothing about. So good luck with that.

For those of you, nearly all apparently, that have not been in the business this is standard practice. Has been, will be and will always be.

Intel: We have this great 13 Watt part.

Manf: We want 7 Watt.

Intel: Okay, under these conditions only, we can validate these chips to operate correctly under these exact conditions. If that is what you want?

Manf: Great! Thanks.

Everybody moves onto the next project. The only difference is Intel has published the numbers for SDP which they normally would not have done. NDA. Not talking allowed.

For the historically minded this is nearly the same thing that happened with the 486/487 outrage from Intel. Idiots, what we normally call the PC press, discovered that one could get the 8087 to actually work on certain 486 chips in various systems that were not supposed to have them. Gasp! Intel must be doing evil deeds.

Umm. Those chips were bought by OEMs without 487 functionality. They were made and the 87 portion may or may not work. It most definitely would NOT work under the conditions Intel required it to be verified as a functional unit.

Intel tests the holy living hell out of the chips. If a portion failed (8087 in 486) the chip was only available as a 486 without FPU and sold as such. Cool. Intel sells chips it would have crushed otherwise, OEMs get a better price, some PC mag hack gets a story, everybody gets to hate Intel and some dweeb thinks his non certified FPU is the real deal. Intel wouldn't continue testing further if that portion already failed (voltage, freq, something). Saves time and time is money.

Today it is easier. Blow the stinking fuse. That piece of the silicon is never going to be used. It didn't pass cert, don't allow the OEM or the customer to ever get to it even if they know which flag to set in the BIOS.

Makes lousy stories though, doesn't it, tin foil boiz.

There is another page to that story but that is for another day. When ignorance is not the order of the day.

This makes the model # mess even more of a mess and something the average Joe will not be looking at. At least Intel is being straightforward enough about it, but not very vocal about it though. This isn't really problem for tech savvy users, but to many people, i7 = better than i5 in all cases and they don't know that there are ULV, dual and quad core versions of the core i7, let alone different models with different features and clock speeds in each tier.

I'm glad I'm aware of this though, it will make shopping for a Windows 8 tablet with the features I want easier. Not that it's going to be easy given what.

Heat dissipation in general is becoming a real problem in CPU architecture anyways. It will be interesting how much lower TDP we'll see with silicon and at which voltage, but that is not a discussion for this thread aside from the fact that it is becoming an issue important enough to throw a wrench into making high clock/low TDP CPUs.

Intel can do whatever kind of hand waving they want, but in my opinion it is still misleading advertising. SDP should remain hidden in the spec sheets where it belongs.

Poor Joe Consumer sees laptop "A" rated at 7 watts (SDP) and laptop "B" rated at 10 watts (TDP) and automatically assumes that "A" will have better battery life because of its lower rated power. Sadly, he is going to get screwed because laptop "A" will actually burn more of his battery crunching that month-end report because its processor will take at least 10/7 times as long to complete the job (assuming his job is compute-limited). During this extra time, laptop "A" will still be having to keep its disk subsystem powered up and probably other chunks as well.

It's hard to compare these to tablet rivals, as these are not SOCs. A chipset is still required, which adds more cost and power demands. Will Haswell be offered as a SOC, or is that left up to Broadwell?

newer Turbo Boost-equipped CPUs can actually exceed their stated clock speeds (and their TDP) for a short amount of time. The idea is that the sooner the CPU can get its work done, the sooner it can go back into a power-sipping idle state

Maybe I'm not completely understanding the trade-offs at work here. A CPU's power usage is proportional to f * V^2, and when the frequency is ramped up, the voltage needs to go up as well (though not as much as the frequency). Therefore the power required rises exponentially with an exponent greater than 1 (the actual value depends on how much additional voltage is required). But the additional computation that can be done per unit time rises with frequency in a roughly linear fashion with a slope < 1 (a CPU running twice as fast will perform a bit less than twice as many calculations because of overhead from the rest of the system).

So the value (extra computational work done) / (extra power consumed) will be less than 1 - You'll get the job done faster, but you'll use more power doing so than you save by going back to sleep sooner. I played around plugging some numbers into a quick speadsheet, but couldn't find any combination that would provide an overall power saving by ramping up the frequency.

Doing stuff faster is clearly desireable, but as far as I can see it will always cost more power. Obviously there's something I'm missing - I'm no microarchitecture engineer. But what is it?

[Just to make it clear: "the sooner the CPU can get its work done," the sooner the work is done, period. As far as I can see, the stuff about "the sooner it can go back into a power-sipping idle state" is irrelevant.]

[Another edit: Actually, I just realised (doh) that the idea of saving power by doing stuff faster (as strongly implied by the quoted sentence) breaks the laws of thermodynamics - So it seems that I'm not missing anything, and this is just a bit of hand-waving from Intel.]

This seems like an elaborate dance around there being two issues for portable — battery-dependent — usage:

standby power, when the chip is doing little or nothing

maximum processing power before the chip melts down.

Most phones, tablets and laptops have a steady, light background activity requirement. Any modern CPU — obviously, including relatively lower-powered ARM chips — can and should keep monitoring wifi for inbound traffic, maybe even make sure that pixels move from Flash to the h.264 decode chips and onto the screen, with no more power than the job requires. Faster won't be better.

And then, there's the recalc on your big spreadsheet, or playing some fancy CPU-bound game, maybe even responding to a reflow triggered by a keystroke in your word processor. That's ALSO a fixed amount of work to be done, but now something that you want completed as quickly as possible.

In both cases, it's Watts/function that matters, but you optimize the former by reducing the watts, and the latter by keeping it in high-power mode for less time. And you maximize any one user's mix by switching smartly between the two.

From the descriptions here, Intel isn't making it any easier to instantly slow down when nothing much is going on, as a power-saving technique. Gonna be up to the OEM to decide how to manage the tradeoff for some hypothetical mix.

It's hard to compare these to tablet rivals, as these are not SOCs. A chipset is still required, which adds more cost and power demands. Will Haswell be offered as a SOC, or is that left up to Broadwell?

Haswell ULV parts are SoCs, the rest are not.

Edit: Though technically, I suppose you'd call them SoPs (System on Package), as they're two pieces of silicon in one BGA package, rather than a single monolithic die.

From the descriptions here, Intel isn't making it any easier to instantly slow down when nothing much is going on, as a power-saving technique. Gonna be up to the OEM to decide how to manage the tradeoff for some hypothetical mix.

The things you're lamenting are the whole point of Haswell.You're welcome.

The latter two values aren't officially defined anywhere on the CPUs' official product pages, but they're there for OEMs whose cooling solutions either exceed or undershoot the TDP value.

Seems Apple decided to exceed the TDP value while undershooting the cooling solution on my Wife's MacBookPro. Though to be fair I've an Acer laptop I use occasionally and that can get pretty warm too, but it doesn't rely on a metal chassis in contact with the users lap as a 'heatsink'.

I dare say what will sort out the good from the bad, with these new chips, will be those manufacturers who choose a barely adequate cooling solution for light use versus a proper cooling solution under normal load.

Underclock it, make it wafer thin and then sell it on battery life. /sigh

Underclock it, make it wafer thin and then sell it on battery life. /sigh

Why is that a bad thing?

That's what most people want. The rise of tablets is just further evidence of the idea that netbooks started: when it comes to computing power, most people just need "good enough". Past that battery life and weight are the most important factors.

This was a little sleazy on Intel's part, on a couple counts. First, when they said 7W chips, the implication is 7W TDP - I don't recall anyone talking much about it in the Pentium 3 days, but starting around the Athlon 64/Pentium 4 days, we started talking about TDP (granted, that may have been when I started paying attention. And was something AMD beat Intel over the head with, until Core 2, when the tables started to turn.) Since then, all this time, when we talk about processor power, we're talking about TDP. Don't tell me when Intel announced 7W Ivy Bridge, you thought anything different.

Second, I was wondering why this came days and days after everyone else already had this same story. Then it turns out Ars got Intel to talk, and they started spewing about PL1 and PL2 states...even though previously Intel pussyfooted around pretending that you couldn't do an apples-to-apples comparison with their other processors, as they're not rated on SDP. Sure sounds to me like that's exactly what Intel does, certifying levels of power their processors are designed to handle (or, that you need to deal with as an OEM that has to come up with a cooling solution for a given processor.)

Now, my posting history will reveal I'm no fan of Intel, and even at that I'll admit they've done some wondrous things over the past few years. However, please stop defending this behemoth corporation - this is what corporations do, pull sleazy shit to make more money. If they want to defend what they've done, let them. If you're not on their payroll, get down off your soapbox.

I would assume that the 'clock speed' intel quotes on ark is the clock speed the processor can sustain under adequate cooling (as defined by the TDP). If that's the case, then I absolutely do think it's dishonest for Intel to quote a 'scenario design power' but not a 'scenario clock speed': an i7-3689Y that operates under a restricted 'scenario' is not really a 1.5 GHz part anymore, and maybe more of a (say) 1.1 GHz part with a 2.6 GHz turbo.

From the descriptions here, Intel isn't making it any easier to instantly slow down when nothing much is going on, as a power-saving technique. Gonna be up to the OEM to decide how to manage the tradeoff for some hypothetical mix.

Uggh.

I'm pretty sure that Intel is doing a LOT of workload modeling, as well as measuring power of various processor function blocks (memory controller, L2/L1 cache, CPU core, GPU blocks etc). And with Haswell they integrate the voltage regulators in order to make power-state transitions that much faster.

So my take on this is that Intel's testing is paying off, and on the way to implementing a modern near-threshold-voltage part, they found that lots of their Ivy Bridge parts can really act like 7-Watt parts.

I would like to know if they are binning "stock" Ivy Bridge parts, or is there more to this? Did they modify the heuristics of the CPU power regulator?

Otherwise Intel gets to pull these types of shenanigans......without much recourse....

I don't see how they're shenanigans. Intel is being rather open about how they came to the 7 watt figure, how they get the chips that meet that figure, and the real TDP for those 7 watt chips.

It's not like my thinkpad had the TDP of the chip on the laptop next to the Core 2 Duo sticker and the Windows Vista sticker. It's not really a number that concerns anyone other than the folks building the system and I'm sure they're taking the true TDP numbers into consideration.

I see it as marketing shenanigans due to one simple fact: in all of the presentations and marketing, they are comparing the SDP of these Y-series processors to the TDP of all others.

Anandtech rightfully called them out on this in an article detailing SDP

Andrew Cunningham / Andrew has a B.A. in Classics from Kenyon College and has over five years of experience in IT. His work has appeared on Charge Shot!!! and AnandTech, and he records a weekly book podcast called Overdue.